The expression “narrowing of a heart valve and/or heart valve insufficiency” is intended to include a functional defect of one or more heart valves which is either genetic or has developed over time due to age or disease. A valve defect of this type might affect each of the four coronary valves, although the valves in the left ventricle (aortal and mitral valves) are affected much more often than the right-hand part of the heart (pulmonary and tricuspid valves). The functional defect can result in narrowing (stenosis), inability to close (insufficiency) or a combination of the two (combined vitium).
The operating principle of medical devices for treating a heart valve insufficiency or stenosis is already generally known in the field of medical technology. Biological or mechanical valve models are currently available as a means for replacing human heart valves. Replacement valves are typically stitched to the base of the native heart valve once the diseased valve has been removed. The procedure requires an opening to be made in the thorax to undertake this intervention, the patient's circulation must be supported by a heart and lung machine and the heart arrested whilst the heart valve prosthesis is implanted. This is a risky surgical intervention which places the patient at considerable risk and involves a long post-operative phase of treatment. In multi-morbid patients in particular, the risk of carrying out such intervention is rarely justifiable.
In more recent times, minimally invasive treatment methods have been developed which are distinctive due to the fact that the intervention can be carried out with a local anaesthetic. This option is based on the use of a self-expanding stent carrying a collapsible heart valve prosthesis which is implanted into the human body by means of an appropriate catheter system. A self-expanding heart valve endoprosthesis of this type can be fed by means of a catheter system through a main artery or vein to the implantation site at the heart. Once the implantation site is reached, the endoprosthesis, such as a stent, is successively unfolded. Once unfolded, the heart valve endoprosthesis can be anchored in the blood vessel, for example, with the assistance of anchoring hooks. The actual heart valve prosthesis is disposed directly in the proximal region of the stent or endoprosthesis.
Patent publication DE 100 10 074 A1 discloses a device for securing and anchoring heart valve prostheses which essentially comprises shaped wire elements connected to one another. Different arches are used as a means of reliably securing and anchoring the heart valve prosthesis. To this end, the device described in this specification has three identical pairs of arches respectively disposed at a distance of 120° apart. These arches are connected to one another by fixed body joints which assume the function of pivot bearings. Arches bent in the opposite direction are also provided, forming lever arms which are of identical length as far as possible, to enable a reliable seating of the arches, even in the event of peristaltic movements of the heart and blood vessel, and afford a reliable seal for an implanted and secured heart valve prosthesis.
With the known solutions there is still a risk of heart valves being incorrectly implanted. In particular, the heart valve prosthesis must be exactly positioned and longitudinally oriented. This requires enormous skill on the part of the surgeon performing the treatment to position a stent carrying a heart valve prosthesis at its proximal end accurately enough in the vicinity of the patient's diseased heart valve to ensure both correct lateral and longitudinal positioning of the heart valve prosthesis.
Amongst other things, incorrect or sub-optimal implantation and positioning of a heart valve prosthesis can lead to inadequate sealing or valve insufficiency which places considerable stress on the ventricle. For example, if a heart valve prosthesis is implanted too far above the actual heart valve plane, this can reduce or even cover and block the outlets of the coronary vessels (coronaries) leading to fatal coronary ischaemia due to heart infarction. Thus, it is absolutely vital that the requirements of both lateral and longitudinal positioning accuracy of a heart valve prosthesis are met.
In the case of conventional minimally invasive implantation techniques where self-expandable heart valve prostheses are introduced to the implantation site at or in the heart through a main artery of the patient, the prosthesis is usually introduced by means of a guide wire and with the aid of catheters. In such a case it is standard practice to use a balloon catheter to expand and open the native heart valves to allow insertion of a catheter. Although it is possible to monitor and control the introduction process during such an intervention, for example with the aid of an X-ray system (heart catheter laboratory=HCL) or with the aid of ultrasound (trans-oesophageal echocardiagram=TEE), the heart valve prosthesis is still of relatively large dimensions in spite of being minimised whilst it is being introduced. It is often not possible to obtain the required positioning accuracy due to restricted ability to manoeuvre, and in particular to ensure correct longitudinal positioning, of the heart valve prosthesis to be implanted with the fixing elements attached to it. If there is a risk that the coronary vessels might close, implanting the heart valve prosthesis in a position angularly offset from the optimum implantation site represents a particular risk for the patient.
When designing a heart valve prosthesis, allowance must specifically be made for the considerable forces which act on the prosthesis, including during the filling phase of the heart cycle (diastole). Reliable anchoring is necessary to prevent the implanted heart valve prosthesis from becoming detached or moving in any direction.
Accordingly, it must be possible to manoeuvre the heart valve prosthesis in the relevant access vessel as efficiently as possible during the implantation process to ensure optimum positioning accuracy on the one hand and, on the other hand, the implanted heart valve prosthesis must be firmly anchored at the implantation site effectively to prevent the prosthesis from subsequently shifting.
Known devices used for the transvascular implantation of heart valve prostheses are often not suitable for easy implantation of a heart valve prosthesis due to the required degree of positioning accuracy. Furthermore, until now it has only been possible to correct an incorrectly positioned heart valve prosthesis that has already been partially implanted with great difficulty—if at all.
These problems have been overcome by means of the medical device of the present invention which has an integral structure cut from a metal tube to provide features that allow accurate positioning and firm anchoring.